Real Ear Measurement for Hearing Aids
May 12, 2021
What is a real ear measurement for hearing aids? The purpose of providing a hearing aid to a user is to assist their declining hearing abilities through the use of amplification. This is performed by recording the results according to different frequencies on the audiogram and then using the audiogram to calculate how much amplification is required for the person to hear optimally. Unfortunately, the calculation is not as simple as it sounds due to the complexity of the structure of the ear canal. No two ears are the same and this results in significant variation in the acoustics of peoples’ ears and the sound that reaches the eardrum.
Due to the variety of ear canals, it is almost impossible for the hearing aid software to come customized according to the acoustics of an individual’s ear canal. The audiogram is used as a starting input, and thereafter information on estimates based on average real-ear data is used to prescribe the amplification for an individual ear.
What is real ear measurement (REM)?
It is necessary to ensure that the hearing healthcare professional or audiologist starts the amplification process from a standardized unit of measurement that is known to be optimized for the users’ ears, and so that any further adjustments are based on amplification that is appropriate for those ears. To do so you measure the amplified sound that is reaching the eardrum.
Real-ear measurements (REM) are also known as probe microphone measurements and are used to determine if the hearing aid user is receiving the optimal level of amplification required at every frequency to achieve the best hearing improvement possible.
During the REM, a thin probe microphone is inserted into the ear canal. This is performed alongside the hearing aid which is worn by the user during the entire process. The hearing healthcare professional then obtains readings of the sound levels that the user is receiving from the hearing aid while listening to standardized recorded speech samples. The readings are usually presented in the form of a graph. The AutoFit function then automatically applies the necessary calculations to match the output of the hearing aid with the REM. This provides a basis from which the hearing healthcare professional can then adjust the sound levels to match target amplification levels based on the hearing aid user’s hearing loss across the speech frequencies.
Disadvantages of real ear measurement
Unfortunately, the costs and accessibility associated with real ear measurement make it difficult to always achieve. The REM process takes time to administer and the user is generally asked to visit the hearing healthcare professional frequently to adjust the hearing aid settings until comfortable amplification is achieved. Real ear measurement equipment is known to be expensive which often means that it will not be conveniently located at all practices. Furthermore, it may lead to an increase in the costs of the hearing aid fittings based on consultation fees in addition to the actual assessment fees. This brings us to what else can be used to achieve a good hearing aid fitting.
How AutoFit is done
AutoFit can be defined as a fitting program that automatically provides and adjusts the hearing aid amplification by applying the real-ear insertion setting without having the hearing healthcare professional manually calculate and match the recommended targets.
How does it work?
During a new hearing aid fitting, the hearing healthcare professional will select a prescriptive formula. These prescriptions are calculated from a number of factors including your hearing loss and help your hearing healthcare provider set up the correct amplification for different types and volumes of sounds. REMs allow the hearing healthcare professional to confirm your hearing aids are applying the right volume for different sounds according to the prescription. These prescriptions can be categorized as linear or non-linear. Linear fitting formulas were designed to prescribe gain for hearing aids with fixed gain and frequency responses across input levels. Non-linear fitting formulas prescribe different amounts of gain depending upon input level and were developed to fit a wide dynamic range of compression hearing aids.
The National Acoustics Laboratories (NAL-NL1) is the linear fitting formula. NAL-NL1 aims to produce all bands of speech at equal loudness. For people with profound hearing loss, research with linear amplification shows us that a systematic departure from equal loudness is necessary: high-frequency bands are made less loud than the others, because of the diminished contribution of the high-frequency bands to the recognition of speech, even when the information within those bands is audible. This NAL-NL1 procedure is an extension of the NAL-RP formula, based on the following assumptions:
- The relative loudness of different speech bands should maximize speech intelligibility.
- The hearing aid patient should perceive speech to be no louder than that which a normal hearing person would perceive.
- The Desired Sensation Level (DSL) is a non-linear prescription. DSL is applied when the objectives of amplification are for the following reasons:
- Avoidance of loudness discomfort during hearing aid use.
- Hearing aid prescription that ensures audibility of important acoustic cues in conversational speech as much as possible.
- Prescription of hearing aid compression that is appropriate for the degree and configuration of the hearing loss, but that attempt to make a wide range of speech inputs available to the listener.
- Accommodation for the different listening requirements within quiet and noisy listening environments.
- Widely recognized fitting for pediatric fittings.
The AutoFit function is offered by most hearing aid manufacturers today. Although it may be available in company-specific programs, it is generally operated off the same interface and essentially provides the same service.
Why use AutoFit?
AutoFit allows the hearing healthcare professional to complete the hearing aid programming and verification process efficiently while maintaining high-quality control over the fitting. It streamlines the fitting process providing the user with a shorter and more comfortable fitting experience so that the hearing healthcare professional can focus on things such as validation and counseling the user to adjust to the hearing aid.
The benefits of AutoFit
- AutoFit assists the hearing healthcare professional to confirm appropriate amplification settings and ensure features in the hearing aid are functioning as they should.
- When REMs cannot be performed the hearing aid can be programmed as best as possible with AutoFit.
- It is much quicker than doing a REM test, in which the patient is required to visit a hearing healthcare professional. This means that the user can use the hearing aid immediately instead of waiting for a REM test.
- AutoFit allows for the hearing aids to be pre-programmed or programmed remotely. This means that the user does not have to physically visit the hearing healthcare professional but can have his hearing aids adjusted accordingly whilst in the comfort of his home.
- The hearing healthcare professional can use AutoFit as the benchmark to provide maximum benefit. If the hearing aids are fit right to the prescription, the user will hear as much sound as possible, without over-amplification.
- Lifestyle suitability: The AutoFit programs usually offer a variety of settings that allow the user to enjoy sound-related hobbies like music, whilst adjusting the sound at a comfortable level.
- Check for hearing aid malfunction and verify features: The user can subjectively measure the performance of features like noise reduction and directional microphones to determine possible malfunction.
The drawback of AutoFit is the possibility of operator errors. When using AutoFit, the correct user profile must be selected. Factors such as experience level, age, audiogram results, etc, should correspond to the parameters used to generate targets for that specific hearing loss.
AutoFit is a quick, accurate, and streamlined tool that reduces complexity while allowing the hearing healthcare professional to maintain control of the verification procedure and to complete it faster than conventional REM. It ensures that the hearing aids are operating properly and are fitted in accordance with the selected fitting rationale, without adding substantial time to the fitting protocol. For those who do not routinely include REM in their fittings, AutoFit represents an easy, fast, and accurate way of increasing the likelihood of hearing aid acceptance and benefit, as well as the decreased likelihood in follow-up visits.